Photovoltaics are currently one of the most research-intensive areas globally in search for new technology to obtain reasonably priced and renewable green energy from sunlight. The technology development nowadays has come very diverse in the photovoltaic field. Among these developed technologies, energy saving devices such as organic light emitting diodes (OLEDs), polymer light emitting diodes (PLEDs), and organic photovoltaic devices (OPVs) are undergoing mass production and applications based on the advanced materials have been developed in recent years. However, there are still some key unsolved problems including low power conversion efficiency and high production cost for the active donor and acceptor materials (typically P3HT and PCBM) in the bulk heterojunction polymer solar cell. Up to now, the power conversion efficiency (PCE) is about 7% using PFN (poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] at Ossila. By using new interface materials and architectures, the PCE of PTB7 (Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-diyl]]) is able to reach about 9%. However, the cost and the synthetic methodology for these polymers are not yet favorable for mass production and commercialization. As such, further improvements are still needed in order to provide ease of processing, higher performance, and lower production cost.
Polythiophene is one of the well-known electrically conducting polymers and it has been an important material for applications in photovoltaic cells, photochemical resists, light emitting diodes, and thin film transistors. For examples, both native polythiophene and regio-regular polythiophenes are well-known conducting polymers for the applications in the fields of energy saving devices.
However, the syntheses of polythiophenes and regio-regular polythiophenes involve lengthy and complicated processes, and cast hindrance for future scale-up and production. Also, solubility is a big problem for solution process of polythiophene.
For example, the most common regio-regular polythiophenes polymer, poly(3-hexylthiophene (P3HT), has reasonable solubility but its production cost is very high and thus limits its applications for organic device fabrication. On the other hand, native polythiophene is cheap but unfortunately it is not soluble in both organic and aqueous solvents. This implies that the native polythiophene is difficult to be processed and thus limit many of its potential applications.